Hyperbranched polymers, in which molecular chains extending from a branching point located in the center have additional branching points, and the number of terminals increases moving away from the center, are expected to be used in various applications due to their large number of terminals and their unique molecular form.
Known examples of hyperbranched polymers include hyperbranched polyester polyols having hydroxyl groups on the terminals of their molecular chains (e.g., specification of U.S. Pat. No. 3,669,939), and attempts have been made to introduce functional groups having even higher reactivity or different forms of reactivity into the molecular chains by using the reactivity of these hydroxyl groups. In particular, multifunctional hyperbranched polymers, in which polymerizable unsaturated double bonds have been introduced into the molecular chains or terminals thereof, are useful as macromonomers, polymer modifiers, functional polymers or multifunctional reaction intermediates.
Numerous attempts have been made to produce polyesters in which polymerizable unsaturated double bonds have been introduced into the molecular terminals of hyperbranched polyester polyols by esterifying the hydroxyl groups of these hyperbranched polyester polyols. Typical examples of these processes are described in (1) to (4) below.    (1) A process in which a hyperbranched polyester polyol is esterified with acrylic acid by dehydration in the presence of methane sulfonic acid (refer to, for example, U.S. Pat. No. 5,418,301).    (2) A process in which a hyperbranched polyester polyol is esterified with methacrylic anhydride in the presence of N,N-dimethylaminopyrridine (refer to, for example, M. Johansson, et al., Journal of Applied Polymer Science (USA), Vol. 75, p. 612 (2000)).    (3) A process in which a hyperbranched polyester polyol is esterified with acryloyl chloride in the presence of triethylamine or N,N-dimethylaminopyrridine (refer to, for example, J. Lang, et al., Polymer (UK), Vol. 42, p. 7403 (2001); and, M. Johansson, et al., Journal of Coating and Technology (USA), Vol. 67, p. 35 (1995)).    (4) A two-stage esterification process in which a hyperbranched polyester polyol is reacted with methacrylic anhydride followed by once separating and purifying the product and then reacting with methacryloyl chloride in the presence of triethylamine (refer to, for example, Q. Wan, et al., Journal of Macromolecular Science Pure and Applied Chemistry (USA), Vol. A37, p. 1301 (2000)).
However, in the case of using a carboxylic acid having a polymerizable unsaturated double bond with low electron density in the manner of (meth)acrylic acid as in the process of (1) above, in addition to the desired dehydration esterification reaction, side reactions occurs in the form of not only a thermal polymerization reaction of the polymerizable unsaturated double bond, but also a nucleophilic addition reaction between hydroxyl groups and polymerizable unsaturated double bonds of the hyperbranched polyester polyol. As a result, there are the problems of increased susceptibility to gelling of the reaction system and a reduction in the number of polymerizable unsaturated double bonds introduced into the molecular terminals.
In addition, in the case of carrying out a dehydration esterification reaction using an acid catalyst as in the process of (1) above, there is also the problem of the occurrence of a side reaction in the form of hydrolysis of the ester bonds of the molecular chains.
Moreover, in the case of esterification reactions using acid anhydrides or acid halides as in each of the processes of (2), (3) and (4) above, there are the problems of increased susceptibility to gelling of the reaction system and a reduction in the number of polymerizable unsaturated double bonds introduced into the molecular terminals in the same manner as the case of (1) above caused by the basic substance used as catalyst or acid receptor.
In addition, in the case of using an acid anhydride or acid halide as in each of the processes of (2), (3) and (4) above, there are also problems in terms of use of the process as an industrial production process as compared with the use of carboxylic ester, including (a) the increased difficulty to obtain such raw materials in industrial scale or limitations on the types of applicable compounds, (b) difficulties in handling such as the need to take precautions regarding reaction with moisture in the air and so forth due to the high reactivity of these compounds, and (c) the need to remove the salts that are formed by the reaction of the acid halide and acid receptors.
If it were possible to introduce polymerizable unsaturated double bonds into the terminals of a hyperbranched polyester polyol by a transesterification without causing the aforementioned problems, such a process would be extremely useful industrially.
However, such an industrially useful transesterification has not been known. The main reasons for this are surmised from (a) and (b) below. Namely, (a) since hyperbranched polyester polyols have extremely high branching density, they are subjected to powerful steric hindrance during the transesterification, thus causing the problem in which the introduction of polymerizable unsaturated double bonds into the terminals does not reach a satisfactory level; and (b) since hyperbranched polyester polyols have a high hydroxyl group content, they are susceptible to the occurrence of nucleophilic addition reactions of the terminal hydroxy groups to polymerizable unsaturated double bonds, thereby resulting in the problem of increased susceptibility to gelling of the reaction system and a reduction in the number of polymerizable unsaturated double bonds introduced into the terminals.
On the other hand, a process is also known in which an alkyl ester of a carboxylic acid having polymerizable unsaturated double bonds in the manner of (meth)acrylic acid alkyl esters and a lower alcohol monomer having 2 to 6 hydroxyl groups in a molecule are reacted by transesterification in the presence of a stanoxane of transesterification catalyst to introduce polymerizable unsaturated double bonds into the lower alcohol monomer terminals (refer to, for example, Japanese Unexamined Patent Application, First Publication No. Hei 9-183751 (U.S. Pat. No. 5,606,103)).
However, the introduction of polymerizable unsaturated double bonds into a hyperbranched polyester polyol is not described in Japanese Unexamined Patent Application, First Publication No. Hei 9-183751 (U.S. Pat. No. 5,606,103). For this reason, even if this Japanese Unexamined Patent Application, First Publication No. Hei 9-183751 (U.S. Pat. No. 5,606,103) exists, it has been unknown as to whether or not the problems of (a) and (b) above can be resolved by the use of a transesterification catalyst composed of stanoxane.